1. Field of the Invention
The invention relates to a pressure vessel containing a fluid medium which is pre-stressed by a mass of gas enclosed in a deformable enveloping body.
2. Description of the Related Art
Enclosed masses of gas are used, inter alia, wherever a medium is to be put, and retained, under pressure but must not be mixed with an open pressure fluid. They are commonly used in piston/cylinder assemblies such as vibration dampers. Such a vibration damper with an enclosed mass of gas is known, for example, from U.S. Pat. No. 3,294,391, wherein the gas is enclosed in a closed cell polyurethane form. The enclosed mass of gas serves for compensating for the volume of the piston and/or of the piston rod penetrating into the vibration damper. A problem is that gas diffuses through the foam into the damping medium.
U.S. Pat. No. 6,116,585 describes a pressure vessel with a deformable enveloping body in which a mass of gas is enclosed by an impermeable wall. Tests have shown that, at certain locations, the enveloping body has stress peaks which adversely affect the service life of the pressure vessel. In the case of a rectangular pressure vessel which is fitted into a round installation position, for example in a vibration damper, random inflections may be produced. A measure taken in order to avoid these inflections, as can be seen from FIGS. 2 and 4, has been to provide connections 27V and thus to achieve sections which run at an angle in the circumferential direction. The above-mentioned stress peaks occurred thereafter.
A further possibility is to use a round pressure vessel, for example as is illustrated in FIG. 5 of U.S. Pat. No. 6,116,585. The disadvantage with this design is that, for each diameter size of the tube enclosing the pressure vessel, it would be necessary to produce a separate pressure-vessel design if the aim is to use the largest possible pressure vessel and/or if one is seeking optimum utilization of space.
The object of the present invention is to achieve a pressure vessel, for an enclosed mass of gas, of which the enveloping body has the smallest possible stress peaks.
According to the invention, the enveloping body is formed by inner and outer walls which are provided with impressed transitions between the sections. The inner and outer walls are not connected at the transitions.
The impressed transition prevents the enveloping body from being exposed to undefined inflections and also prevents excessive friction from occurring on the walls. Correspondingly rounded transitions minimize the stress states in the enveloping body, with the result that the service life of the enveloping body can be extended to a decisive extent. In a further advantageous configuration, the impressed transition is designed as a radius.
A further measure according to the invention for minimizing the stress states in the enveloping body consists in the wall being designed with an expansion profile. It is precisely when the wall has a material with a very low level of expansion, e.g. a metal foil, that the expansion of the enveloping body can be achieved by an expansion profile. An expansion profile is to be understood as all folds in the wall which allow a change in length by the fold being straightened out.
The practical configuration of the expansion profile also has to be considered from an economic point of view. A compromise will be sought between production outlay and expansion capacity of the expansion profile. Extensive tests have shown that an expansion profile with a sinusoidal cross section is particularly well suited since, in this case, only extremely small additional stresses are introduced into the foil/sheet material.
It may also be advantageous for the impressed transition between the sections, which are aligned at an angle to one another, and the expansion profile to form a superposed profile. Superposed profile is to be understood in the manner that, for example, rather than interrupting the expansion profile, the impressed formation between the sections, which are aligned at an angle to one another, also contains the expansion profile.
In terms of short cycle times during the production of the pressure vessel, provision may be made for the expansion profile to be restricted to a strip in the region of the impressed transition.
In order to achieve the best possible action of the expansion profile, the latter extends transversely to the longitudinal axis of the enveloping body. In the case of pressure vessels which are subjected to particularly high loading, provision may also be made for the expansion profile to comprise a plurality of individual expansion profiles.
For reasons of strength, provision is made for the expansion profile comprising a plurality of individual expansion profiles to bound lozenge-shaped wall segments. It has proven advantageous here if the expansion profiles run obliquely in relation to the longitudinal axis of the pressure vessel and the resulting corner points of the lozenge-shaped wall segments are located on a pitch circle and on lines parallel to the longitudinal axis.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.